Thursday, July 20, 2017

Earth's Shadow

Many people have seen Earth's shadow, but were unaware of its presence. After the sun sets, or before it rises, there's about a 20 minute window to watch Earth's shadow projected on the atmosphere. It appears as a slightly darker blue band above the horizon with a reddish band above it.

I produced a short time-lapse movie of Earth's shadow in the west as the sun rises in the east. The movie has two parts. The first part is in visible light, or how we would see it with our eyes. The second part is through the eyes of near infrared. Interesting that the slightly smoky skies we're dealing with in the Treasure Valley prevents our eyes from seeing the anticrepuscular rays but that NIR cuts right through the haze. What are anticrepuscular rays? Well, crepuscular rays are the dark shadow of clouds projected into the atmosphere as lines or rays. Anticrepuscular rays are those cloud shadows projected onto the opposite end of the sky. They point to the anti-solar point, or the point in the sky are is opposite the sun.